An enzyme prepared from chick pectoral muscle was found to promote the synthesis of canosine and anserine from their constituent amino acids. Assay involved incubation of the enzyme with either carboxy- 14C histidine or 1-methylhistidine (plus ⨿-alanine), and subsequent destruction of excess free labeled amino acid with ninhydrin. Residual radioactivity represented incorporation into peptides. The latter were chacterized by paper chromatography, by hydrolysis with carnosinase, and by butanol extraction following diazotization (in the case of carnosine). The optimum pH for both carnosine and anserine formation was about 7.5 and both Mg ++ and ATP were required in each case. Experiments with 14C-β-alanine and D and L-histidine showed that only the natural form of this latter amino acid was effective for the synthetic process.